Cell-cell interactions in early mammalian development are a poorly understood sequence of morphogenetic events. These cell-cell interactions which include changes in cell shape, in cell movement and in cell adhesion, are dependent on certain properties of the cell surface properties can result in deficient cell-cell interactions leading to abnormal development. These observations have raised the intriguing questions whether cell surface properties and cytoskeletal elements are functionally linked and whether such a linkage controls cell surface-cytoskeletal activities guiding the temporal sequence of morphogenetic events that constitute normal development. Based on the hypothesis that cell surface-cytoskeletal interactions are essential for morphogenetic events, the aims of these proposed experiments are: 1) To establish possible transmembrane interactions between cytoskeletal elements and stage-specific cell surface antigens (detected by anti-blastocyst serum and anti-hCG serum) using mouse preimplantation development as a test system. 2) To study the influence of these interactions on morphogenetic events, such as compaction and the morula-to-blastocyst transformation, during preimplantation mouse development in vitro.